Emissive display with photo-switchable polarization

ABSTRACT

A novel emissive display assembly incorporates a photo-switchable polarizer that is switchable between an active, polarizing, state and an inactive, non-polarizing, state depending on the predetermined level of intensity of UV light in the ambient light and enhance the viewable quality of the emissive display by minimizing or eliminating UV light reflection on the emissive display.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of the copending U.S. patentapplication Ser. No. 14/554,286, filed on Nov. 26, 2014.

FIELD

Aspects of the present disclosure relate generally to displays and moreparticularly to emissive displays such as organic light emitting diode(OLED) displays.

BACKGROUND

With the proliferation of electronic devices in modern society,technologies for displaying information to people have become moreimportant than ever. Advances in display technology from bulky cathoderay tube (CRT) displays to liquid crystal displays (LCDs), lightemitting diode (LED) displays and other displays have fueled thepopularity and ubiquity of displays in the marketplace. Emissivedisplays, such as organic light emitting diode (OLED) displays, havebecome increasingly popular in recent years as they have manyadvantageous attributes such as relatively low weight, low cost, and lowenergy consumption compared to other types of displays. Emissivedisplays are increasingly found in mobile electronic devices such asnotebook computers, tablet computers, smartphones, cameras, etc., andare increasingly being used in outdoor environments. The outdoor viewingscenario, however, presents increased unpredictability in terms oflighting conditions and increased range of possible ambient lightconditions. These factors associated with outdoor use, particularlyregarding strong ambient lighting, are particularly challenging for theemissive displays because of ambient light reflections on the reflectivelayers in the displays.

In order to improve their viewability, emissive displays often employcircular polarizers to reduce ambient light reflection by the reflectivelayers in the displays, particularly in bright ambient light conditions.However, circular polarizers reduce the light output from the emissivedisplay by at least 50% because of the circular polarizer's handedness.When there is little or no ambient light, the circular polarizer reducesthe emissive display's own light emission and reduce the brightness ofthe emissive display.

SUMMARY

In some embodiments of the present disclosure, an emissive displaymodule includes a substrate, an array of light emissive elementsprovided over the substrate, and a photo-switchable polarizer providedover the array of light emissive elements. The photo-switchablepolarizer is switchable between an active state and an inactive statedepending on the level of intensity of UV light in ambient light of theemissive display module.

In some embodiments, an emissive display assembly includes an emissivedisplay panel having a viewing surface, and a photo-switchable polarizerlocated in front of the viewing surface. The photo-switchable polarizeris switchable between an active state and an inactive state depending onthe level of intensity of UV light in ambient light of the emissivedisplay assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The following will be apparent from elements of the figures, which areprovided for illustrative purposes and are not necessarily to scale:

FIG. 1 is a cross-sectional view of an emissive display assembly inaccordance with some embodiments of the present disclosure;

FIG. 2 is a cross-sectional view of an emissive display assembly inaccordance with some other embodiments;

FIG. 3 is a schematic cross-sectional illustration of the emissivedisplay module according to an embodiment;

FIG. 4 is a schematic cross-sectional illustration of the emissivedisplay module according to another embodiment; and

FIG. 5 shows the chemical structures according to Formula 1 and Formula2 that are examples of the reversibly photo-switchable polarizingmaterials disclosed herein.

DETAILED DESCRIPTION

This description of the exemplary embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description. In the description, relativeterms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,”“below,” “up,” “down,” “top” and “bottom” as well as derivative thereof(e.g., “horizontally,” “vertically,” “downwardly,” “upwardly,” etc.)should be construed to refer to the orientation as then described or asshown in the drawing under discussion. These relative terms are forconvenience of description and do not require that the apparatus beconstructed or operated in a particular orientation.

Various embodiments of the present disclosure address theabove-described challenges associated with emissive displays. Byproviding a polarizer to make an emissive display easier to view inbright ambient light settings (e.g., outdoor lighting environment) andenabling the polarization functionality to be toggled on or offdepending on ambient lighting conditions, various embodiments yield anefficient display solution that performs well in various lightingscenarios.

FIG. 1 is a simplified schematic cross-sectional view of an emissivedisplay assembly 200A according to an embodiment. The emissive displayassembly 200A comprises an emissive display panel 210 having a viewingsurface 212; and a reversibly photo-switchable linear polarizer 230Alocated in front of the viewing surface 212. The reversiblyphoto-switchable linear polarizer 230A is switchable between an activestate and an inactive state depending on the level of intensity ofultraviolet (UV) light in the ambient light of the emissive displayassembly 200A. When the reversibly photo-switchable linear polarizer230A is in the active state, the photo-switchable polarizer linearlypolarizes the light passing therethrough. On the other hand, when thereversibly photo-switchable linear polarizer 230A is in the inactivestate, the photo-switchable polarizer allows light to pass throughwithout polarizing the light.

The term “front” as used herein refers to the side of the emissivedisplay panel 210 or the emissive display module 300A, 300B facing theviewer 500.

In this embodiment, the emissive display assembly 200A further comprisesa quarter-wave plate 220 located between the photo-switchable linearpolarizer 230A and the emissive display panel 210. A quarter-wave plate220 converts linearly polarized light into circularly polarized lightand vice versa.

Referring to FIG. 2, in another embodiment, an emissive display assembly200B comprises an emissive display panel 210 and a reversiblyphoto-switchable circular polarizer 230B provided in front of theviewing surface 212. The photo-switchable circular polarizer 230B isswitchable between an active state (polarizing state) and an inactivestate (non-polarizing state) depending on the level of intensity of UVlight in the ambient light of the emissive display assembly 200B. Whenin its active state, the photo-switchable circular polarizer 230Bcircularly polarizes the light passing therethrough.

In the various embodiments described herein, the emissive display panel210 includes an array of OLED light emissive elements 215 that form theimages seen by the viewer 500 through the viewing surface 212. Theviewing surface 212 can be formed by a transparent protective layer 217.

Referring to FIG. 3, according to another embodiment, an emissivedisplay panel 210A comprising an emissive display module 300A isdisclosed. The emissive display module 300A comprises a substrate 102,an array of OLED light emissive elements 109 provided on the substrate102, and a reversibly photo-switchable linear polarizer layer 116Aprovided over the array of OLED light emissive elements 109. Similar tothe reversibly photo-switchable polarizers 230A, 230B, the reversiblyphoto-switchable linear polarizer layer 116A is switchable between anactive polarizing state and an inactive non-polarizing state dependingon the level of intensity of UV light in the ambient light of theemissive display module 300A.

Because the photo-switchable polarizer layer 116A is a linear polarizer,the emissive display module 300A further comprises a quarter-wave plate110 located between the photo-switchable linear polarizer layer 116A andthe array of OLED light emissive elements 109. The emissive displaypanel 210A can include a transparent protective layer 217 for protectingthe emissive display module 300A as shown in FIG. 3.

Referring to FIG. 4, according to another embodiment, an emissivedisplay panel 210B comprising an emissive display module 300B isdisclosed. The emissive display module 300B comprises a substrate 102,an array of OLED light emissive elements 109 provided on the substrate102, and a reversibly photo-switchable circular polarizer layer 116Bprovided over the array of OLED light emissive elements 109. Thereversibly photo-switchable circular polarizer layer 116B is switchablebetween an active polarizing state and an inactive non-polarizing statedepending on the level of intensity of UV light in the ambient light ofthe emissive display module 300B. The emissive display panel 210B caninclude a transparent protective layer 217 for protecting the emissivedisplay module 300B as shown in FIG. 4.

In various embodiments described herein, the substrate 102 may be formedfrom any one or more of various materials, including silicon, glass,plastic, ceramics, and metal suitable for OLED substrates. Although thedetails of various sub-components of the array of OLED light emissiveelements 215 and 109 are not shown or described in detail, one ofordinary skill in the art would readily understand that the OLED lightemissive elements 215 and 109 would include such structures andcomponents as the OLED pixels, electrodes for delivering the drivingcurrent to the OLED pixel arrays, power supplies, etc. for the array ofOLED light emissive elements 215, 109 to form images viewed by theviewer 500.

In various embodiments described herein, the reversibly photo-switchablepolarizer (any of 230A, 230B, 116A, 116B) comprises one or more ofreversibly photo-switchable polarizing material(s) that is/are in anactive polarizing (ON) state when the level of intensity of the UV lightin the ambient light is greater than or equal to a predetermined leveland in an inactive non-polarizing (OFF) state when the level ofintensity of the UV light in the ambient light is less than thepredetermined level. For example, reversibly photo-switchable polarizingmaterial can be selected so that the predetermined level of theintensity of the UV light in the ambient light that would switch thephoto-switchable polarizing material between the ON/OFF states is 0.1W/m² (at 365 nm). In such example, the photo-switchable polarizingmaterial will switch to its ON state when the intensity of the UV lightin the ambient light is ≧0.1 W/m² (at 365 nm) and switch to its OFFstate when the UV light intensity in the ambient light is <0.1 W/m2 (at365 nm).

Activation and deactivation of the photo-switchable polarizingmaterial(s) can be effected by molecular rearrangement and alignment ofthe photo-switchable polarizing materials Linear, rod-like materialssuch as conjugated azobenzene type compounds would induce linearpolarization. Chiral materials such as twisted aromatics (e.g.,hexahelicene) would induce circular polarization. In some embodiments,the degree of polarization is controllable because the level ofmolecular arrangement in the photo-switchable polarizer depends on theamount of UV light in the ambient light. The aligned state and therandom state are in equilibrium. More materials are in the aligned(polarization) state when there is more UV light. For example, at UVirradiance of 0.1 W/m² (at 365 nm), ≧90% of the materials are in thealigned state, and at 0.01 W/m² (at 365 nm), ≦10% of the materials arein the aligned state.

In the active polarizing state, ambient light reflection in the emissivedisplay assembly 200A/200B or emissive display module 300A/300B isreduced, making the displayed light output easier for viewer 500 to viewin bright outdoor conditions, for example. In some embodiments,absorption by the reversibly photo-switchable polarizing material(s)occurs at wavelengths of 420 nm or higher. This can ensure minimalabsorption of OLED emitted light in some embodiments, leading tounblocked, full utilization of the OLED emission

In one embodiment, the device comprising the display and thephoto-switchable polarizer is equipped with a sensor which detects theUV intensity of the UV irradiance level in the ambient light and adjuststhe display brightness accordingly. For example, when the sensor detectsa UV irradiance of ≧0.1 W/m² (at 365 nm), the display is adjusted to ahigh brightness mode, e.g., at an intrinsic OLED brightness of 1000cd/m² and extrinsic brightness of 500 cd/m², (assuming the polarizerblocks 50% of the light) as the photo-switchable polarizer will be atthe ON state. When the sensor detects a UV irradiance of ≦0.01 W/m² (at365 nm), the display is adjusted to a low brightness mode, e.g., at anintrinsic OLED brightness of 200 cd/m² and extrinsic brightness of 200cd/m² as the photo-switchable polarizer is at the OFF state. On theother hand, if a regular, always “on” polarizer is used, even when theUV irradiance is ≦0.01 W/m² (at 365 nm), in order to reach an externalbrightness of 200 cd/m², the intrinsic brightness needs to be at 400cd/m². Energy saving can be achieved.

In the inactive non-polarizing state, the reversibly photo-switchablepolarizer (any of 230A, 230B, 116A, 116B) is transparent to the emissionof light (does not significantly absorb emitted light). Thus, insufficiently dim indoor conditions (for example), the polarizationfunctionality is switched off. Thus, in various embodiments polarizationis only activated when needed.

The reversibly photo-switchable polarizing material(s) used in thephoto-switchable polarizer in various embodiments may include anymaterial that exhibits variable polarization based on ambient UV light.Such materials are known for use in, for example, photochromiceyeglasses that darken upon exposure to specific types of light. By wayof non-limiting examples, such reversibly photo-switchable materialsinclude one or more azobenzene compounds doped in a polymer materialsuch as poly-methylmethacrylate and poly-vinyl polymer may be used. Anexample of such an azobenzene compound has a structure according toFormula 1 shown below

In another example, the reversible photo-switchable material can be oneor more polymers with azobenzene derivative pendant groups such ascompounds having the structure according to Formula 2 shown below mayalso be used.

In Formula 1 and Formula 2 shown in FIG. 5, R^(a), R^(b), R¹-R⁸ andA¹-A⁷ are each independently selected from the group consisting ofhydrogen, deuterium, halide, alkyl, haloalkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, thioalkoxy, aryloxy, thioaryloxy, amino, arylamino,diarylamino, carbazolyl, silyl, halosilyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof; L is a linker; and x is an integer≧1 and y is integer ≧0.

The previous description of the embodiments is provided to enable anyperson skilled in the art to practice the disclosure. The variousmodifications to these embodiments will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other embodiments without the use of inventive faculty. Thepresent disclosure is not intended to be limited to the embodimentsshown herein, but is to be accorded the widest scope consistent with theprinciples and novel features disclosed herein.

What is claimed is:
 1. An emissive display assembly comprising: anemissive display panel having a viewing surface; and a photo-switchablepolarizer located in front of the viewing surface, wherein thephoto-switchable polarizer is switchable between an active state and aninactive state depending on a level of intensity of UV light in ambientlight of the emissive display assembly.
 2. The emissive display assemblyof claim 1, wherein the photo-switchable polarizer is configured to bein the active state when the level of intensity of the UV light in theambient light is greater than or equal to a predetermined level and thephoto-switchable polarizer is configured to be in the inactive statewhen the level of intensity of the UV light in the ambient light is lessthan the predetermined level.
 3. The emissive display assembly of claim1, wherein the photo-switchable polarizer is a circular polarizer. 4.The emissive display assembly of claim 3, wherein the photo-switchablepolarizer is configured to be in the active state when the level ofintensity of the UV light in the ambient light is greater than or equalto a predetermined level and the photo-switchable polarizer isconfigured to be in the inactive state when the level of intensity ofthe UV light in the ambient light is less than the predetermined level.5. The emissive display assembly of claim 1, wherein thephoto-switchable polarizer is a linear polarizer, the emissive displayassembly further comprising a quarter wave plate located between thephoto-switchable polarizer and the emissive display panel.
 6. Theemissive display assembly of claim 5, wherein the photo-switchablepolarizer is configured to be in the active state when the level ofintensity of the UV light in the ambient light is greater than or equalto a predetermined level and the photo-switchable polarizer isconfigured to be in the inactive state when the level of intensity ofthe UV light in the ambient light is less than the predetermined level.7. The emissive display assembly of claim 1, wherein thephoto-switchable polarizer comprises one or more azobenzene compoundsdoped in a polymer material selected from poly-methylmethacrylate orpoly-vinyl polymer.
 8. The emissive display assembly of claim 7, whereinthe azobenzene compound has a structure according to Formula 1:

wherein R^(a), R^(b), and R¹-R⁸ are each independently selected from thegroup consisting of hydrogen, deuterium, halide, alkyl, haloalkyl,cycloalkyl, heteroalkyl, arylalkyl, alkoxy, thioalkoxy, aryloxy,thioaryloxy, amino, arylamino, diarylamino, carbazolyl, silyl,halosilyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof.
 9. The emissive display assembly of claim 1, wherein thephoto-switchable polarizer comprises one or more polymer compounds withazobenzene derivative pendant groups, the one or more polymer compoundshaving a structure according to Formula 2:

wherein R^(a), R^(b), R¹-R⁸ and A¹-A⁷ are each independently selectedfrom the group consisting of hydrogen, deuterium, halide, alkyl,haloalkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, thioalkoxy,aryloxy, thioaryloxy, amino, arylamino, diarylamino, carbazolyl, silyl,halosilyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof; L is a linker; and x is an integer ≧1 and y is integer ≧0. 10.The emissive display assembly of claim 1, further comprising a sensorthat detects the level of intensity of UV light in the ambient light andadjusts the emissive display panel's brightness depending on whether thelevel of intensity of UV light in the ambient light is greater than orequal to a predetermined level or less than the predetermined level. 11.The emissive display assembly of claim 1, wherein the emissive displaypanel includes an array of OLED light emissive elements.